Various developments in the area of wireless communication have proven that cooperative communication enhances performance in wireless environments. The idea of cooperative transmission emerged from the realization that spatial diversity may counteract the effects of fading, shadowing, attenuation and interference of wireless communication channels. For example, as presented in G. Foschini and M. Gans, “On limits of wireless communications in a fading environment when using multiple antennas,” Wireless Pers. Commun., pp. 311-335, 1998; and I. Telatar, “Capacity of multi-antenna Gaussian channels,” Eur. Trans. Telecommun., vol. 10, no. 6, pp. 585-595k November/December 1999, spatial diversity was achieved in single communication links via the use of multiple antennas.
However, in wireless networks, the effect of multiple antennas may be realized through the combined use of antenna resources of different nodes. This observation lead to the notion of message relaying presented, for example, in A. Sendonaris, E. Erkip, and B. Aazhang, “User cooperation diversity—Part I: system description,” IEEE Trans. Commun., vol. 51, pp. 1927-1938. November 2003; A. Sendonaris, E. Erkip, and B. Aazhang. “User cooperation diversity—Part II: implementation aspects and performance analysis,” IEEE Trans. Commun., vol. 51, pp. 1939-1948. November 2003; J. N. Laneman, D. N. C. Tse, and G. W. Wornell, “Cooperative diversity in wireless networks: efficient protocols and outage behavior,” IEEE Trans. Inform. Theory, vol. 50, pp. 3062-3080, December 2004; G. Kramer, M. Gastpar, and P. Gupta, “Cooperative strategies and capacity theorems for relay networks,” IEEE Trans. Inform. Theory, vol. 51, no. 9 pp. 3037-3063, September 2005; G. Kramer, I. Marie, and R. D. Yates, Cooperative Communications, vol. 1, no. 3-4. “Foundations and Trends in Networking”, Flanover, Mass.: NOW Publishers Inc., 2006; A. Host-Madsen, “Capacity bounds for cooperative diversity,” IEEE Trans. Inform. Theory, fol. 52, no, 4, pp. 1522-1544. April 2006; and A. S. Avestirnehr and D. N. C. Tse. “Outage capacity of the fading relay channel in the low-SNR regime,” IEEE Trans. Inform. Theory, vol. 53, no. 4, pp. 1401-1415. April 2007.
The message relaying concept recently has received a great deal of attention. Most of the work on cooperative relaying has been focused on the Physical Layer, which is an actual hardware layer (lowest layer) in the Open Systems Interconnection (OSI) reference model. This model is a seven layer architecture arranged from the lower levels starting with the Physical Layer to the higher levels, including in order a Data Link Layer (which includes the Logical Linc Control (LLC) and Media Access Control (MAC) sub-layers), a Network Layer, a Transport Layer, a Session Layer, a Presentation Layer, and an Application Layer.
A. K. Sadek, et al. in the publication “Cognitive multiple access via cooperation: protocol design and performance analysis,” IEEE Trans. Inform. Theory, vol. 53, no. 10, pp. 3677-3697, October 2007, have provided the evidence that performance gains may be achieved even when the cooperation scheme is implemented at the Network Protocol Layer level. The Network Protocol Layer is the IP (Internet Protocol) supporting layer which routes messages (packets) across the network boundaries using the best path available between the source host to the destination host based on their addresses.
In Sadek, et al., a relay node is placed in between the source nodes and the destination node to relay packets from the source nodes. The system thus introduces extra relay nodes which merely perform a relaying function for the source nodes, thereby burdening the system with pure relays.
The extra pure relay node may not always be available. Moreover, in order for Sadek, et al.'s relaying method to attain performance improvement for all source nodes, the relay node must have a better channel to the destination than all the source nodes. This has never been suggested in Sadek, et al.
A concept was studied in S. Biswas, et al., “Opportunistic routing in multi-hop wireless networks”, ACM SIGCOMM, vol. 34, no. 1, pp. 69-74, January 2004, which selects the best user among network users to relay the packet. However, the publication focuses on characterizing the total number of transmissions required to deliver a single packet between a pair of nodes, and therefore does not address the scheduling problem within a wireless network, since there is only a single packet at any one time in the network. No suggestion or analysis has been presented in S. Biswas, et al. for the case where the intermediate relay nodes would also have their own packets to deliver. In addition, the results of the analysis are based solely on simulation.
It is therefore would be highly desirable to provide a cooperative transmission technique in a more realistic environment where all source nodes are active participants transmitting their own packets and relaying packets of other source nodes with a lesser quality of the channels, and where multiple packets coexist is the system.